Studies of a Novel Catalytic System of B(C6F5)3 and Ammonium Hydrochlorides
Received date: 2015-06-05
Online published: 2015-07-17
Supported by
Project supported by the National Science Foundation of China (Nos. 21072157, 20702041), and the Key Laboratory Foundation of Leshan Normal University (Z1308).
In modern practice, frustrated Lewis pairs (FLPs) are well-known to exhibit unique chemical properties in respect to H2 activation. Additionally, CO2 catalytic reduction and related catalytic hydrogenations of unsaturated bonds have also been widely concerned. This paper describes designation and studies of a novel FLP catalyst system, in which the Lewis base component is introduced as an amine hydrochloride (not a free amine), while the Lewis acid component is retained [tris(pentafluorophenyl)borane, B(C6F5)3 (BCF)]. With a hydridosilane as a source of the hydride, this novel system, at first, presents a new facile synthetic approach to ammonium hydridoborates [R3NH]+[HBCF]-. Remarkably, that irrespective of the bulkiness of the ammonium component, various primary, secondary and tertiary ammonium salts with HBCF- anion can all be prepared by the suggested procedure under mild conditions and in high yields. At the same time this system may serve as a powerful tool for selective and exhaustive reduction of organic carbonyl compounds and even CO2 down to alkanes and methane, respectively. Comparison of the 1H NMR spectra of the starting hydrochlorides, the intermediate ammonium chloroborates [R3NH]+[ClBCF]-, and [R3NH]+[HBCF]- reveals that the appearance of the NH signals is strongly dependent upon the nature of the counterion. While in the parent chlorides signals of these protons are observed as broad singlets or multiplets due to the quadrupolar relaxation on the adjacent 14N nucleus, in the spectra of their [HBCF]- analogues these signals exhibit distinct fine structure due to the spin-spin coupling with the 14N [1J(14N-H)≈50 Hz; 1︰1︰1 triplets]. The latter is indicative of the increase of the symmetry of the electric field at the 14N nucleus location along with the decrease of the degree of ammonium/anoin interaction. The chemical reactivity of these [HBCF]- analogues is interesting matched with their NH signals．
Hu Xi , Tian Chong , Borzov Maxim , Nie Wanli . Studies of a Novel Catalytic System of B(C6F5)3 and Ammonium Hydrochlorides[J]. Acta Chimica Sinica, 2015 , 73(10) : 1025 -1030 . DOI: 10.6023/A15050371
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